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    Subject[PATCH 5.13 264/266] media: v4l2-core: explicitly clear ioctl input data
    Date
    From: Arnd Bergmann <arnd@arndb.de>

    commit 7b53cca764f9b291b7907fcd39d9e66ad728ee0b upstream.

    As seen from a recent syzbot bug report, mistakes in the compat ioctl
    implementation can lead to uninitialized kernel stack data getting used
    as input for driver ioctl handlers.

    The reported bug is now fixed, but it's possible that other related
    bugs are still present or get added in the future. As the drivers need
    to check user input already, the possible impact is fairly low, but it
    might still cause an information leak.

    To be on the safe side, always clear the entire ioctl buffer before
    calling the conversion handler functions that are meant to initialize
    them.

    Signed-off-by: Arnd Bergmann <arnd@arndb.de>
    Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
    Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
    Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/media/v4l2-core/v4l2-ioctl.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/drivers/media/v4l2-core/v4l2-ioctl.c
    +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
    @@ -3124,8 +3124,10 @@ static int video_get_user(void __user *a
    if (copy_from_user(parg, (void __user *)arg, n))
    err = -EFAULT;
    } else if (in_compat_syscall()) {
    + memset(parg, 0, n);
    err = v4l2_compat_get_user(arg, parg, cmd);
    } else {
    + memset(parg, 0, n);
    #if !defined(CONFIG_64BIT) && defined(CONFIG_COMPAT_32BIT_TIME)
    switch (cmd) {
    case VIDIOC_QUERYBUF_TIME32:

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